Shape characteristics and particle size distribution: Effects on flowability and floodability of select grain dust types

Authors: BARRETTO, ROSELLE - Kansas State University; SILIVERU, KALIRAMESH - Kansas State University; CASADA, MARK - US Department Of Agriculture (USDA)

Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2023
Publication Date: 12/5/2023
Citation: Barretto, R., Siliveru, K., Casada, M.E. 2023. Shape characteristics and particle size distribution: Effects on flowability and floodability of select grain dust types. Biosystems Engineering. https://doi.org/10.13031/ja.15378.
DOI: https://doi.org/10.1016/j.biosystemseng.2022.11.005

Interpretive Summary: High dust concentrations that occur with grain handling operations can cause serious problems, including health and safety risks from dust inhalation and increased risk of explosions with dust clouds. Dust suspension in confined space is a key ingredient leading to these problems and which must be controlled to prevent dust inhalation and explosions. We investigated the grain dust properties that affect that suspension of dust, including flowability and floodability of the dust. Dust samples from five grain types (wheat, corn, soybean, rice, and milo) showed significant differences with soybean dust being the most flowable of the five types and milo dust the least flowable. However, all five dust types were categorized as having bad or very bad flowability using the Carr Index, indicating that all will be difficult to handle in bulk without bridging problems and will require specialized equipment to achieve good flow. The floodability indices varied significantly between dust types, but four of the five grain dusts showed high enough floodability that rotary seals could be (rice, wheat, and corn) needed or definitively are (soybeans) needed on equipment to prevent dust from escaping, leading to dispersion potentially into confined spaces. Only milo dust had sufficiently low floodability that rotary seals would not be expected to be needed. These results improve our understanding of grain dust properties and their release to the atmosphere, which can be used to improve grain handling procedures for better health and safety.

Technical Abstract: Dust explosions occur when the dust exceeds its minimum explosible concentration (45-150 g m-3) in the presence of confinement, oxidizer, dispersing agent, and ignition source. These components have long been documented in the literature but studies on dust properties that affect suspension in a confined space, such as flowability and floodability, are lacking. To address this, dust samples from five grain types (wheat, corn, soybean, rice, and milo) with particle size <450 µm were obtained and tested in five replicates for mean particle size, particle size distribution, and various shape characteristics (high sensitivity circularity, convexity, elongation, solidity, and aspect ratio) using Morphologi G3. Flowability and floodability indices were determined using Carr indices chart based on aerated and packed bulk density ('_p) measurements; angles of repose, spatula, fall, and difference; compressibility; cohesion; and dispersibility in the Hosokawa Powder Tester PT-R. Results showed significant differences in packed bulk density, cohesion, elongation, and aspect ratio among the five grain dust types. Soybean dust exhibited the highest flowability (34.70) and floodability (64.25) indices while milo dust exhibited the lowest (flowability index, 11.60; floodability index, 9.70). A very strong positive correlation was observed between dispersibility and floodability index and very strong negative correlation between cohesion and flowability index. High sensitivity circularity also strongly influenced the packed bulk density and floodability index.